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  • Other Sources  (17)
  • 1
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    An upwind multigrid algorithm for calculating flows on unstructured grids (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: An algorithm is described that calculates inviscid, laminar, and turbulent flows on triangular meshes with an upwind discretization. A brief description of the base solver and the multigrid implementation is given, followed by results that consist mainly of convergence rates for inviscid and viscous flows over a NACA four-digit airfoil section. The results show that multigrid does accelerate convergence when the same relaxation parameters that yield good single-grid performance are used; however, larger gains in performance can be realized by doing less work in the relaxation scheme.
    Keywords: AERODYNAMICS
    Type: In: AIAA Computational Fluid Dynamics Conference, 11th, Orlando, FL, July 6-9, 1993, Technical Papers. Pt. 2 (A93-44994 18-34); p. 1035, 1036.
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  • 2
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    Comparison of two Navier-Stokes codes for attached transonic wing flows (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 29; 101-107
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  • 3
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    Strake camber and thickness design procedure for low alpha supersonic flow (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 27; 481-487
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  • 4
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    Euler analysis of a High-Speed Civil Transport concept at Mach 3 (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 28; 239-245
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  • 5
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    Aerodynamic Design on Unstructured Grids for Turbulent Flows (1997)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An aerodynamic design algorithm for turbulent flows using unstructured grids is described. The current approach uses adjoint (costate) variables for obtaining derivatives of the cost function. The solution of the adjoint equations is obtained using an implicit formulation in which the turbulence model is fully coupled with the flow equations when solving for the costate variables. The accuracy of the derivatives is demonstrated by comparison with finite-difference gradients and a few example computations are shown. In addition, a user interface is described which significantly reduces the time required for setting up the design problems. Recommendations on directions of further research into the Navier Stokes design process are made.
    Keywords: Aerodynamics
    Type: NASA-TM-112867 , NAS 1.15:112867
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  • 6
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    An Implicit Upwind Algorithm for Computing Turbulent Flows on Unstructured Grids (1994)
    In:  CASI
    Details
    Publication Date: 2018-06-02
    Description: An implicit, Navier-Stokes solution algorithm is presented for the computation of turbulent flow on unstructured grids. The inviscid fluxes are computed using an upwind algorithm and the solution is advanced in time using a backward-Euler time-stepping scheme. At each time step, the linear system of equations is approximately solved with a point-implicit relaxation scheme. This methodology provides a viable and robust algorithm for computing turbulent flows on unstructured meshes. Results are shown for subsonic flow over a NACA 0012 airfoil and for transonic flow over a RAE 2822 airfoil exhibiting a strong upper-surface shock. In addition, results are shown for 3 element and 4 element airfoil configurations. For the calculations, two one equation turbulence models are utilized. For the NACA 0012 airfoil, a pressure distribution and force data are compared with other computational results as well as with experiment. Comparisons of computed pressure distributions and velocity profiles with experimental data are shown for the RAE airfoil and for the 3 element configuration. For the 4 element case, comparisons of surface pressure distributions with experiment are made. In general, the agreement between the computations and the experiment is good.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: Computers Fluids; Volume 23; No. 1; 1-21
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  • 7
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    Numerical study to assess sulfur hexafluoride as a medium for testing multielement airfoils (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A methodology is described for computing viscous flows of air and sulfur hexafluoride (SF6). The basis is an existing flow solver that calculates turbulent flows in two dimensions on unstructured triangular meshes. The solver has been modified to incorporate the thermodynamic model for SF6 and used to calculate the viscous flow over two multielement airfoils that have been tested in a wind tunnel with air as the test medium. Flows of both air and SF6 at a free-stream Mach number of 0.2 and a Reynolds number of 9 x 10(exp 6) are computed for a range of angles of attack corresponding to the wind-tunnel test. The computations are used to investigate the suitability of SF6 as a test medium in wind tunnels and are a follow-on to previous computations for single-element airfoils. Surface-pressure, lift, and drag coefficients are compared with experimental data. The effects of heavy gas on the details of the flow are investigated based on computed boundary-layer and skin-friction data. In general, the predictions in SF6 vary little from those in air. Within the limitations of the computational method, the results presented are sufficiently encouraging to warrant further experiments.
    Keywords: AERODYNAMICS
    Type: NASA-TP-3496 , L-17401 , NAS 1.60:3496
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  • 8
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    An Euler analysis of a High-Speed Civil Transport (HSCT) concept at Mach 3 (1989)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A marching Euler solver, GEM3D, was used to predict the Mach 3 flow field for the wing and body of a High-Speed Civil Transport concept. The analysis focused on a typical cruise lift coefficient of 0.1 at alpha = 3 deg. The Euler solution indicated that embedded shocks formed on the upper surface of the inboard wing panel and at the leading-edge of the outboard wing panel, due to its supersonic leading edge condition. According to a simple static-pressure criterion, the embedded wing upper-surface shocks were sufficiently strong to separate a turbulent boundary layer. Comparison of aerodynamic coefficients from the Euler solver with those from linear theory shows that the linear theory estimates of lift and drag are optimistic, which would lead to optimistic estimates of cruise range.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 89-2174
    Format: text
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  • 9
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    A strake design method for supersonic speeds and low lift (1987)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A method is presented for the design of a strake for a forebody typical of supersonic aircraft at typical cruise (low lift) conditions, in order to ensure attached flow on the strake upper surface. The method systematically varies strake camber and thickness until an attached flow surface pressure distribution is achieved. Surface pressures are computed by the full potential flow solver, NCOREL. The high-alpha flowfield of the strake is also investigated experimentally and computationally; a large vortex is noted on the strake leeside, together with a pair of vortices on the forebody upper centerline. The effect of sideslip on the high-alpha flowfield is also discussed.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 87-2638
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  • 10
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    Relative efficiency and accuracy of two Navier-Stokes codes for simulating attached transonic flow over wings (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Two codes which solve the 3-D Thin Layer Navier-Stokes (TLNS) equations are used to compute the steady state flow for two test cases representing typical finite wings at transonic conditions. Several grids of C-O topology and varying point densities are used to determine the effects of grid refinement. After a description of each code and test case, standards for determining code efficiency and accuracy are defined and applied to determine the relative performance of the two codes in predicting turbulent transonic wing flows. Comparisons of computed surface pressure distributions with experimental data are made.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TP-3061 , L-16811 , NAS 1.60:3061
    Format: application/pdf
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